We present the first statistical analysis of kinematically resolved, spatially extended $\rm Ly\alpha$ emission around z = 2–3 galaxies in the Keck Baryonic Structure Survey (KBSS) using the Keck Cosmic Web Imager (KCWI). Our sample of 59 star-forming galaxies (zmed = 2.29) comprises the subset with typical KCWI integration times of ∼5 h and with existing imaging data from the Hubble Space Telescope and/or adaptive optics-assisted integral field spectroscopy. The high-resolution images were used to evaluate the azimuthal dependence of the diffuse $\rm Ly\alpha$ emission with respect to the stellar continuum within projected galactocentric distances of ≲30 proper kpc. We introduce cylindrically projected 2D spectra (CP2D) that map the averaged $\rm Ly\alpha$ spectral profile over a specified range of azimuthal angle, as a function of impact parameter around galaxies. The averaged CP2D spectrum of all galaxies shows clear signatures of $\rm Ly\alpha$ resonant scattering by outflowing gas. We stacked the CP2D spectra of individual galaxies over ranges of azimuthal angle with respect to their major axes. The extended $\rm Ly\alpha$ emission along the galaxy principal axes is statistically indistinguishable, with residual asymmetry of ≤2 per cent (∼2σ) of the integrated $\rm Ly\alpha$ emission. The symmetry implies that the $\rm Ly\alpha$ scattering medium is dominated by outflows in all directions within 30 kpc. Meanwhile, we find that the blueshifted component of $\rm Ly\alpha$ emission is marginally stronger along galaxy minor axes for galaxies with relatively weak $\rm Ly\alpha$ emission. We speculate that this weak directional dependence of $\rm Ly\alpha$ emission becomes discernible only when the $\rm Ly\alpha$ escape fraction is low. These discoveries highlight the need for similar analyses in simulations with $\rm Ly\alpha$ radiative transfer modelling.

中文翻译：

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KBSS-KCWI 调查：扩展的 Ly α 晕与 z ∼ 2-3 处的星系方位角之间的联系

我们使用凯克宇宙网络成像仪 (KCWI) 在凯克重子结构调查 (KBSS) 中对 z = 2-3 星系周围的运动学分辨、空间扩展的 $\rm Ly\alpha$ 发射进行了首次统计分析。我们的 59 个恒星形成星系样本（zmed = 2.29）包括典型 KCWI 积分时间约为 5 小时的子集，以及来自哈勃太空望远镜和/或自适应光学辅助积分场光谱的现有成像数据。高分辨率图像用于评估扩散 $\rm Ly\alpha$ 发射相对于 ≲30 适当 kpc 的投影半心距离内的恒星连续体的方位角依赖性。我们引入了圆柱投影二维光谱 (CP2D)，它映射了指定方位角范围内的平均 $\rm Ly\alpha$ 光谱轮廓，作为星系周围撞击参数的函数。所有星系的平均 CP2D 光谱显示了流出气体引起的 $\rm Ly\alpha$ 共振散射的清晰特征。我们在相对于它们的主轴的方位角范围内堆叠了单个星系的 CP2D 光谱。沿星系主轴的扩展 $\rm Ly\alpha$ 发射在统计上无法区分，剩余不对称性为积分 $\rm Ly\alpha$ 发射的 ≤2% (~2σ)。对称性意味着 $\rm Ly\alpha$ 散射介质在 30 kpc 范围内由各个方向的流出物支配。同时，我们发现对于 $\rm Ly\alpha$ 发射相对较弱的星系，$\rm Ly\alpha$ 发射的蓝移分量沿星系短轴稍微强一些。我们推测，只有当 $\rm Ly\alpha$ 逃逸分数较低时，$\rm Ly\alpha$ 发射的这种弱方向依赖性才变得可辨别。这些发现强调了在 $\rm Ly\alpha$ 辐射传输模型的模拟中进行类似分析的必要性。